# Series-Parallel

Discussion in 'Homework Help' started by keyboardcowboy, Dec 31, 2012.

1. ### keyboardcowboy Thread Starter New Member

Dec 31, 2012
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0

Well this is not a HOMEWORK question, just something i came across..by using a circuit simulator i have found the current consumed @ 5V i.e 407mA and according to OHM LAW

R=V/I

=5/407=12.2 ohm

Solving the circuit manually i have come up with 12.02 ohm using series-parallel combination and Y-DELTA transformation..
Can anyone help me out

2. ### WBahn Moderator

Mar 31, 2012
18,064
4,904
Help with what?

The two values differ by 1.5%. Why do you think it isn't round off error?

3. ### keyboardcowboy Thread Starter New Member

Dec 31, 2012
25
0
hmm, i did not think about that..maybe it is (thank GOD i still remember the basics)...but could you try and solve it just to be on the safe side

4. ### Jony130 AAC Fanatic!

Feb 17, 2009
3,990
1,115
Well I got this result
Rt = 565/46 = 12.2826087Ω

5. ### WBahn Moderator

Mar 31, 2012
18,064
4,904
I worked it using Mesh Current Analysis and, assuming I didn't make any mistakes, I got 12.283Ω ( 5Ω*(2 + 21/46) to be exact). So my current with 5V applied would have been 407.08mA. This agrees well with the simulation result. In fact, if the sim result was 407mA, that is 12.285Ω which you should have rounded to 12.3Ω (if you weren't going to report it to three sig figs).

My guess is that you just haven't been careful enough with your roundoff error. In general, you should carry at least two sig figs more in your calculations than you intend to report the result to.